Mod.A. Bio Lec4: TCA cycle

Question 1

What is the link reaction between glycolysis and TCA cycle? (catalyzed by, coenzymes (5))

Answer 1

Oxidative decarboxylation of pyruvic acid

This reaction is catalyzed by the pyruvate dehydrogenase complex. (يختصر PDC أو PDH )

• PDC is composed of three enzymes ,

contains five coenzyme : TPP (thiamine), lipoic acid, FAD, NAD+ and CoASH

Question 2

Allosteric Inhibition of PDH (3)

Answer 2

1- acetyl coa

2-atp

3- nadh

phosphorylation

Question 3

Allosteric Activation of PDH (5)

Answer 3

1-AMP
2-ADP
3-CoASH
4-NAD+
5-Ca2+

by dephosphorylation

Question 4

Deficiency of PDH results in:?

Symptoms?

Answer 4

congenital lactic acidosis

because pyruvate is converted to acetyl-CoA at a decreased rate, meaning pyruvate will instead be converted to lactate by lactate dehydrogenase.

Symptoms :neonatal onset, hypotonicity, lethargy خمول , neurodegeneration, muscle spasticity تشنج عض ي ل , and early death

Question 5

TCA cycle (site,goal,importance)

Answer 5

• Site : mitochondrial matrix
  Mitochondria of all tissue cells except RBCs, which not contain mitochondria.

** الهدف : oxidize acetyl CoA to CO2, H2O and energy.

** أهميتها :
1- الحصول على Some ATP is produced - More NADH.
حيث NADH goes on to make more ATP in electron transport and oxidative phosphorylation.
2- plays a major role in gluconeogenesis, transamination, deamination, and lipogenesis.
خاصة في The liver (is the only tissue)

Question 6

Rate controlling enzymes of TCA

Answer 6

1- citrate synthase
2-a ketoglutarate dehydrogenase
3-isocitrate dehydrogenase

Question 7

Total energy produced from 1 acetyl coa

Answer 7

12

Question 8

Total energy produced from 1 pyruvate

Answer 8

15

Question 9

Total energy produced from 1 glucose

Answer 9

38

Question 10

Functions of kreb’s cycle

Answer 10

1. It is the final pathway for complete oxidation of all food-stuffs CHO, lipids and protein which are converted to acetyl CoA.
2. It is the major source of energy for cells except cells without mitochondria as RBCs.
3. It is the major source of succinyl CoA which used for perphyrine and Hb synthesis.

Question 11

Citrate is used to

Answer 11

synthesize FA

Question 12

alpha ketoglutarate is used to

Answer 12

synthesize non essential a.a

Question 13

oxaloacetate is used to

Answer 13

synthesize glucose

Question 14

Filling reactions of kreb’s cycle ? (4)

Answer 14

PEP carboxylase
-converts PEP to oxaloacetate

•Pyruvate carboxylase
-converts pyruvate to oxaloacetate

AST
converts aspartate to oxaloacetate

•Malic enzyme
converts pyruvate into malate

Question 15

defects in TCA cycle happen at which enzymes ? (3)

Answer 15

1. Succinate dehydrogenase (SDH)
2. Fumarase (fumarate hydratase: FH)
3. Isocitrate dehydrogenase (IDH)

Question 16

Isocitrate Dehydrogenase mutation

Answer 16

mutated in acute myeloid leukemia.

This mutation causes IDH2 to catalyze its reaction to a final product
of 2-hydroxyglutarate instead of the correct alpha-ketoglutarate

results in DNA and histone hypermethylation, therefore causing epigenetic changes which make way for neoplasia.

2-hydroxyglutarate is often a cancer biomarker in pediatric patients الأطفال with inborn errors of metabolism